The bandwidth shortage increasingly experienced by mobile carriers has motivated the exploration of the underutilized Millimeter Wave (mmWave) frequency spectrum between 3G and 300G Hz for the next generation broadband cellular communication networks. The available spectrum of mmWave band is two hundred times greater than the conventional cellular system. The mmWave wireless network uses directional communications with narrow beams and can support multi-gigabit data rate. The underutilized bandwidth of the mmWave spectrum has wavelengths ranging from 1 mm to 100 mm. The very small wavelengths of the mmWave spectrum enable large number of miniaturized antennas to be placed in a small area. Such miniaturized antenna system can produce high beamforming gains through electrically steerable arrays generating directional transmissions.
With recent advances in mmWave semiconductor circuitry, mmWave wireless system has become a promising solution for real implementation. However, the heavy reliance on directional transmissions and the vulnerability of the propagation environment present particular challenges for the mmWave network. In general, a cellular network system is designed to achieve the following goals: 1) Serve many users with widely dynamical operation conditions simultaneously; 2) Robust to the dynamics in channel variation, traffic loading and different QoS requirement; and 3) Efficient utilization of resources such as bandwidth and power. Beamforming adds to the difficulty in achieving these goals.
Analog beamforming is a good candidate for application in mmWave beamforming wireless systems. It provides array gain for compensating severe pathloss due to harsh wireless propagation environment, and removes the need for training channel response matrix between multiple antenna elements at TX/RX sides. To provide moderate array gain, large number of array elements may be needed. Different beamformers can have different spatial resolution, i.e., beamwidth. For example, a sector antenna can have shorter but wider spatial coverage, while a beamforming antenna can have longer but narrower spatial coverage. At a base station (BS) side, a sector/cell is served by a manageable number of coarse control beams. All control beams in a cell is referred to as control region. Other finer-resolution BS beams are termed dedicated beams that need to be trained before usage. All dedicated beams in a cell is referred to as dedicated region. Beam training mechanism ensures that BS beam and UE beam are aligned for data communication.
Control region is more crowded than dedicated region. Control beams carry more overhead channels, e.g., to broadcast information. Control beams have wider angular coverage than dedicated beams, thus more UE to serve. On the other hand, dedicated beam transmission is more resource-efficient. Dedicated beam has higher array gain and has less crowded control channel. The resource ratio of overhead channel to data channel for a UE in dedicated beam is lower than that of control beam. Dedicated beam transmission is possible only in dedicated resources. Moreover, DRX is essential for UE power consumption perspective. However, user traffic could be very bursty so that DRX mechanism in existing technologies cannot be applied directly in mmWave systems.
A solution for properly utilizing and balancing different beams with power saving mechanism in mmWave beamforming systems is sought.